1. Field of the Invention
The present invention relates to labelling and, more particularly, to a method and apparatus for feeding labels to the cavity of a mold for adherence to articles formed within the mold.
2. Description of the Related Art
In-mold labels are known in which a label is placed within the cavity of a mold and in which the label becomes adhered to the surface of an article formed within the mold. A typical application is in the production of blow molded containers. A preprinted label with heat activated adhesive is placed against the inner surface of a mold cavity and held by vacuum ports in the mold. The mold is closed, and a plastic blank is heated and inflated within the mold. The hot plastic presses against the label, thus activating the adhesive and causing the label to be adhered to the outer surface of the newly molded container. The mold is opened and the labelled container is ejected from the mold.
In the past, in-mold labels have been furnished as stacks of precut, discrete labels. In the manufacture of such labels, individual oversized labels are printed and piled in a stack. A die cutter cuts through the stack to trim all the labels in the stack to final size. The stack of the precut labels is loaded in a magazine, and a pick and place device, such as a vacuum cup on an articulated arm, engages the frontmost label in the stack, removes the label from the stack, and transfers the label to the interior of the mold where the label is held in position by vacuum holes for adhesion to the container or article to be blow molded.
In the past, paper has been used as the material for precut, stacked in-mold labels. However, the use of paper complicates any recycling of the materials since the paper of the label must be separated from the plastic of the container. Therefore, plastic sheet material has been substituted for paper as the material used for precut, stacked in-mold labels. However, the use of plastic labels in this manner has given rise to other drawbacks.
Plastic sheet material tends to stretch during the printing process and in other handling steps, especially when subject to heat. As a result, the placement of the printed indicia on the sheet may be nonuniform. When the printed sheets are stacked and subsequently die cut in a stack, the indicia on each label may not lie in proper registration with the die cutter and the edges of the cut label.
When plastic labels are stacked and die cut to final size while stacked, the pressure of the die cutter causes the overlying edges of the plastic labels to weld or adhere together, thus making it more difficult to separate and remove single labels from the stack for transfer to a mold.
Plastic material tends to accumulate static electricity which causes the plastic labels to adhere together in the stack, thus complicating the removal of single labels from a magazine. A dusting of corn starch has been used to reduce static electricity, but the corn starch tends to clog the vacuum holes which hold the labels in the molds.
Plastic label material is more expensive than paper. Also, a relatively thicker, stiffer, and more costly plastic sheet material must be used so that the labels are capable of being stacked and die cut as a stack, and of withstanding the handling associated with stacking and dispensing.
Furthermore, the plastic label material must not only have sufficient stiffness, but must also be compatible with the container material. As a resulte, the range of suitable materials is limited.